Effects of power and electrical current density variations in an in vitro endometrial ablation model

To investigate the thermal effects of electrical power and waveform on uterine tissue in vitro, using the gynecologic resectoscope with a 2.5-mm roller-bar electrode.

The power setting was increased in a serial fashion using both the modulated or damped (coagulating) and unmodulated or undamped (cutting) current to ablate endometrial uterine tissue, using a technique similar to that employed in clinical situations. The power setting ranged from 20-75 W with the modulated waveform and 40-160 W with the unmodulated waveform. Measurements of tissue damage were made by staining for hematoxylin and eosin and the respiratory enzyme dehydronicotinamide adenine dinucleotide phosphate diaphorase.

The amount of thermal injury present correlated linearly with the amount of wattage used for either current. Regardless of the power used, the maximum amount of injury into the myometrium was 4.2 mm, representing 19% of the uterine wall thickness, well within the limits of safety. Destruction to 3 mm of myometrium was achieved significantly more often using an unmodulated waveform at greater than 90 W (chi 2, P = .03).

Although the correlation between power and tissue damage achieved statistical significance, the relationship was weak; less than 12% of the observed variation was attributable to increasing wattage. Power and waveform alone do not appear to be clinically significant determinants of the amount of thermal injury occurring during endometrial ablation.